How to make use of multicore computing resources to accelerate the block cryptography applications has become a common concern problem. And the block cryptography applications have not yet been explored in procedure level speculation thoroughly. This paper proposes a procedure level speculation mechanism for accelerating block cryptography applications, including execution model, synchronization strategy and analysis method, etc. It also takes RC5 and AES for examples to analyze their potential speedups and memory accessing characteristics. The experimental results show that: (1) in procedure level speculation, the block cryptography applications can get a nearly liner growth speedup under ECB mode, (2) the severe inter-thread data dependence violations is the key factor that badly affect the system performance under CBC, CFB and OFB modes.